[llvm] [PEI] Materialize registers before calling insertZeroCallUsedRegs (PR #214147)

[Bill Wendling via llvm-commits]

bwendling wrote:

> Does insertZeroCallUsedRegs need to be called where it is? Can it be moved after the existing scavengeFrameVirtualRegs call? Seems weird to need to call scavengeFrameVirtualRegs in two places.

I'm not sure the reasoning I had to place `insertZeroCallUsedRegs` where it's at. It might have been "this looks like a good place." If it works when moving to after the existing `scavengeFrameVirtualRegs` call, then that's fine.

https://github.com/llvm/llvm-project/pull/214147